Impact of urbanization on groundwater quality and recharge using hydrogeochemical and environmental tracers in the San Salvador Aquifer

Abstract

Chemical and isotopic characteristics of the urban aquifer of San Salvador, drinking water (SAP) and wastewater systems (SAR), were evaluated in an area of 362 km² to detect if leakages in both are recharging the aquifer and modifying its natural quality. An amount of 37 sampling sites that includes deep wells and springs, as well as two water import systems of the Metropolitan Area of San Salvador (AMSS) were sampled in 2007, 2009 and 2017. Samples were analyzed for major ions and stable isotopes of d¹⁸O and d²H. While the SAR was characterized by chemical tracers of Cl^- and NO₃^-. Results show the existence of four water groups: Groups A (Ca-Mg-HCO₃), B (Mg-Ca-HCO₃) and D (Na-Ca-HCO₃) have meteoric water as their main source of recharge, hence, they do not evidence urban influence in their quality; group C (Na-Ca-HCO₃ and Na-Mg-HCO₃) is derived from group A, flows under the AMSS and suggests three sources of recharge: Direct natural recharge due to precipitation along urban recharge from SAP and SAR leakages. An expensive “fictitious sustainability” could be perceived due to the quantitative contribution of the SAP recharge, which would be hiding the effects of the extractions and consequently the decrease of groundwater levels in the aquifer. Meanwhile, SAR recharge forewarn of a potential entry of pollutants into the aquifer that must be monitored and treated in a timely manner to avoid contamination. The study highlights the need of an integrated urban water resources management.